9.14: importance of the water cycle

Why is water so important to life?

All organisms need it for survival

What are the stages in the water cycle?

Evaporation, condensation, precipitation, transpiration

What is evaporation?

Heat (usually from the sun) is used to change water as a liquid to water vapour, a gas

What is condensation?

When water vapour cools, it is condensed into tiny droplets of liquid water

What is precipitation?

Water falls from the clouds back to the ground as rain, sleet and snow

What is transpiration?

The loss of water vapour from the leaves of a plant

What is surface runoff?

Much water will be absorbed into the ground after rainfall, but some can run along the surface of the ground

What is infiltration?

This occurs when water that has fallen as precipitation is absorbed into the ground, which can then be stored within underground rocks called aquifers

What is potable water?

Water that is safe to drink

How can water be made potable?

Distillation/desalination and reverse osmosis

What is desalination?

Turning seawater into potable water

Why can’t seawater be drunk?

It has a high salt content

What happens during desalination?

Seawater is boiled, then cooled and condensed to form pure water

What are disadvantages to desalination?

It is expensive as large amounts of thermal energy are needed to heat the seawater, it increases the use of fossil fuels (which are non renewable resources) and it increases CO2 emissions from burning fossil fuels, contributing to global warming

Which countries often use desalination?

Some Middle Eastern countries which have little rainfall due to desert conditions but high wealth due to oil reserves

What is the process of reverse osmosis?

Saltwater is forced at high pressure into a vessel with a partially permeable membrane. The pressure causes water molecules to move in the opposite direction to osmosis from a concentrated salt solution (lower water concentration) to a lower salt solution (higher water concentration). Water molecules pass across the membrane leaving the salt behind

What happens to water found naturally?

It has a low salt content so doesn’t need to have any salt removed, but is treated with chemicals, filtered to remove dirt, pathogens and toxic substances, then treated to remove the taste by removing other non toxic substances

Where does most potable water in the UK come from?

Naturally occurring freshwater sources, such as rainwater